1. Field of the Invention
The present invention relates to a lamp current control device, and more particularly, to a lamp current control device which is suitable for LCD backlight.
2. Description of the Prior Art
FIG. 1 shows a structure of a conventional single lamp control circuit. In the single lamp control circuit, a transformer 11 has a primary side connected to an electronic power switch 12 and a secondary side of transformer 11 connected with one end of a lamp 13. The other end of lamp 13 is connected to one end of a pulse width modulation (PWM) IC 14, and then the other end of PWM IC 14 is connected to the electronic power switch 12 to form a single lamp control circuit 1. PWM IC 14 detects and processes a feed back current signal to obtain a control signal, and outputs the control signal to the electronic power switch 12 to control a pulse width outputted by the electronic power switch 12, thereby controlling and maintaining a uniform brightness of the lamp 13. However, the above-mentioned circuit is only suitable for controlling single lamp circuit. In the case of controlling multiple lamps, the number of transformers has to be increased proportionally, thus increasing the manufacturing cost and limiting the use of the single lamp control circuit.
FIG. 2 illustrates a structure of a conventional double lamps control circuit. In the double lamps control circuit, a transformer 21 has a primary side connected to an electronic power switch 22 and a secondary side of transformer 21 connected with one end of each one of two lamps 23. The other end of each lamp 23 is connected to one end of PWM IC 24, and then the other end of PWM IC 24 is connected to the electronic power switch 22 to form a double lamps control circuit 2. PWM IC 24 detects and processes a feed back current signal to obtain a control signal, and outputs the control signal to the electronic power switch 22 to control a pulse width outputted by the electronic power switch 22, thereby controlling and maintaining a uniform brightness of each lamp 23. However, the above-mentioned circuit is only suitable for controlling double lamps circuit. In the case of controlling multiple lamps, the number of transformers has to be increased proportionally, and the number of the feedback circuit has to be increased as well, thus increasing the manufacturing cost and limiting the use of the double lamps control circuit.
FIG. 3 illustrates a structure of a conventional long lamp control circuit. In the long lamp control circuit, each one of the two transformers 31 has a primary side connected to an electronic power switch 32 and a secondary side with one end connected to one end of a lamp 33. The other end of the secondary side of each transformer 31 is connected to one end of PWM IC 34, and then the other end of PWM IC 34 is connected to the electronic power switch 32 to form a long lamp control circuit 3. PWM IC 34 detects and processes a feed back current signal to obtain a control signal, and outputs the control signal to the electronic power switch 32 to control a pulse width outputted by the electronic power switch 32, thereby controlling and maintaining a uniform brightness of long lamp 33. However, the above mentioned circuit is only suitable for controlling long lamp circuit, besides, it is necessary to use two transformers for one long lamp. In the case of controlling multiple lamps, the number of transformers has to be increased proportionally, and the number of the feedback circuit has to be increased as well, thus increasing the manufacturing cost and limiting the use of the long lamp control circuit.
Therefore, the convention lamp current control devices mentioned above present several shortcomings to be overcome.
In view of the above-described deficiency of conventional transformers, after years of constant effort in research, the inventor of this invention has consequently developed and proposed a lamp current control device in the present invention.